Spongiform encephalopathies are neurodegenerative diseases caused by misfolding ofÂ normal cellular prion proteins. A 2014 case of variant Creutzfeldt-Jacob prion disease in the United States was probably caused by eating beef from animals withÂ bovine spongiform encephalopathy (BSE), or mad cow disease.
Human spongiform encephalopathies are placed into three groups:Â infectious,Â familialÂ or genetic, andÂ sporadic, distinguished by how the disease is acquired initially.Â In the mid 1980s, a prion disease called bovine spongiform encephalopathy appeared in cows in the United Kingdom. It is believed to have been transmitted to cows by feeding them meat and bone meal, a high protein supplement prepared from the offal of sheep, cattle, pigs, and chicken. Some of theÂ animals prepared for feedÂ likely had a prion disease.Â Cases of variant Creutzfeld-Jakob disease, a new spongiform encephalopathyÂ of humans, began to appear in 1994 in Great Britain. TheyÂ were characterized by a lower mean age of the patients (26 years), longer duration of illness, and differences in other clinical and pathological characteristics. Variant Creutzfeldt-Jakob disease (vCJD) is caused by prions transmitted by the consumption of cattle with bovine spongiform encephalopathy.
In late 2012 a male Texas resident began showing symptoms of depression and anxiety, followed by delusions, hallucinations, and other changes in behavior. Over the next 18 months the patient’s condition deteriorated, leading to inability to ambulate or speak, and after several episodes of aspiration pneumonia and sepsis the patient died. During the illness prion disease was suspected, but tests for this condition were negative. After death, examination of brain biopsies revealed typical prion plaques, and misfoldedÂ prion proteins were found in urine, confirming the diagnosis of variant Creutzfeldt-Jacob disease.
The source of the patient’s prion disease was likely consumption of contaminated beef from cows with bovine spongiform encephalopathy. The patient probably acquired the infectionÂ in Russia, Lebanon, orÂ Kuwait, three countries that had received BSE-contaminated beef from the UK, and and where he had previously lived. He residedÂ in the US for 14 years before developing symptoms, an incubation period consistent with models of the vCJD epidemic.
This Texas patient is the fourth worldwide since 2012 to be diagnosed with vCJD; the others were from the UK and France. There are likely to be additional cases of vCJD in the future: surveys of archived appendix tissues in the UK show that 1 in 2,000 persons born during 1941-1985 have asymptomatic vCJD infection. These individuals could transmit the misfolded prion proteins to others via transplantation, blood transfusion, or surgical instruments (prion infectivity is not destroyed by autoclaving).
The good news is that vCJD is rare: there have been 230 reported cases of vCJD worldwide caused by consumption of BSE beef. The bad news is that vCJDÂ willÂ probably continue to appear in humans for many years, not only from the aftermath of the BSE epidemic. Rare cows spontaneously develop BSE, and because cattle are slaughtered before disease symptoms are evident, contaminated meat could enterÂ the food supply.